1. Field of the Invention
The present invention relates to a vehicle driven with powers respectively output to front wheels and to rear wheels, a power output apparatus and a driving system mounted on such a vehicle, and control methods of the vehicle, the power output apparatus, and the driving system.
2. Description of the Prior Art
One known structure of a power output apparatus for a hybrid vehicle equipped with a hydraulic brake unit includes a driveshaft, an engine linked with the driveshaft via a planetary gear mechanism, a generator connected to the planetary gear mechanism, and a motor linked with the driveshaft via a transmission (see, for example, Japanese Patent Laid-Open No. 2006-187158). In the case of a change of a speed change state in the transmission from a Hi gear position to a Lo gear position under regenerative control of the motor for braking the vehicle, this power output apparatus sets a torque command of the motor to gradually decrease a regenerative braking force to zero and compensates for a resulting decrease in total braking force with a braking force applied by the hydraulic brake unit. This aims to prevent a torque shock (variation in total braking force) caused by a speed change in the transmission.
The power output apparatus of this known structure is not restricted to front-wheel drive vehicles or rear-wheel drive vehicles but is also applicable to four-wheel drive vehicles by distributing the power output to the driveshaft into front wheels and rear wheels. The cited reference, however, does not disclose braking control in the case of a change of the speed change state of the transmission under regenerative control of the motor in a four-wheel drive vehicle equipped with such a power output apparatus.